Operation of a fuel injector may be described by a transfer function or gain that describes fuel injector flow or that describes an amount of fuel injected based on a fuel injector pulse width. Individual fuel injectors of a fuel system may be operated according to a single transfer function to provide a desired engine air-fuel ratio. However, there may be differences between fuel injectors that cause the amount of fuel injected to the engine to be different than is expected. For example, deposits may form at injector nozzles, thereby reducing fuel flow through the fuel injector. In other examples, one fuel injector may have slightly different nozzle holes that increase or decrease fuel injector flow as compared with fuel flow of a nominal fuel injector (e.g., a fuel injector that operates according to the fuel injector transfer function). Differences between expected fuel injector flow and actual fuel injector flow may lead to engine air-fuel errors. Further, if the fuel injector is operated in a ballistic operating region (e.g., a non-linear fuel flow region) where the fuel injector does not flow at a same rate as the fuel injector flows in a linear flow range, the fuel injector may exhibit additional fuel flow differences between its output and the fuel injector transfer function. For at least these reasons, it may be desirable to re-characterize fuel injector flow during a life cycle of an engine.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for fueling a cylinder, comprising: operating a fuel injector in a ballistic operating region supplying fuel to the cylinder; and adjusting a control parameter of the fuel injector in response to exhaust lambda and a fuel fraction provided to the cylinder by the fuel injector; and operating the fuel injector based on the adjusted control parameter.
By adjusting a fuel injector transfer function or gain based on exhaust lambda and a fuel fraction provided to a cylinder, it may be possible to provide the technical result of improve engine air-fuel control of a cylinder that includes two fuel injectors per cylinder without introducing significant fueling errors to an engine. For example, a first fuel injector may be commanded to provide a large fraction of fuel to a cylinder while a second fuel injector is commanded to provide a small fraction of fuel to a cylinder. Consequently, if the second fuel injector's transfer function or gain includes errors, the engine air-fuel ratio will only vary by a fraction of the error. Further, the fraction of error introduced by the second fuel injector's transfer function may be separated from the engine air-fuel ratio by dividing the engine exhaust lambda (e.g., air-fuel ratio divided by stoichiometric air-fuel ratio) by the fuel fraction provide by the second fuel injector. The second fuel injector's transfer function error may then be adapted or adjusted out of the second fuel injector's transfer function. In this way, fuel injector transfer function errors may be reduced even in ballistic operating ranges without causing large engine air-fuel ratio disturbances.
The present description may provide several advantages. In particular, the approach may reduce engine air-fuel errors. Further, the approach may allow a fuel injector to be operated at pulse widths that were heretofore avoided because of non-linear fuel injector behavior. Further still, the approach may reduce engine emissions and improve catalyst efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.